Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$111.86	12.834%	$126.2161	$126.22	$126.20	$126.20
Purchase #2	$33.36	5.463%	$35.1825	$35.18	$35.20	$35.20
Purchase #3	$31.88	10.177%	$35.1244	$35.12	$35.10	$35.10
Purchase #4	$51.82	10.558%	$57.2912	$57.29	$57.30	$57.30
Purchase #5	$78.54	5.407%	$82.7867	$82.79	$82.80	$82.80
Purchase #6	$243.78	10.772%	$270.04	$270.04	$270.05	$270.00
Purchase #7	$62.98	6.451%	$67.0428	$67.04	$67.05	$67.00
7 purchase totals =	$614.22		$673.6837	$673.68	$673.70	$673.60